JP5696540B2 - AD converter, dial input device, and resistance-voltage conversion circuit - Google Patents

Description

  The present invention relates to an AD converter having a double integration AD converter, a dial input device, and a resistance-voltage conversion circuit.

  FIG. 3 is a diagram showing a configuration of a general double integration AD converter 10. The double integration AD converter 10 includes a switch 11, an integrator 12, a comparator 13, and a LOGIC block 14. The switch 11 selectively outputs one of the input first integrated voltage Vin and the second integrated voltage −Vref according to an instruction from the LOGIC block 14. The integrator 12 includes an operational amplifier 12a, a resistor 12b, and a capacitor 12c. In the operational amplifier 12a, the output from the switch 11 is input to the negative terminal via the resistor 12b, and the positive terminal is grounded. The operational amplifier 12a integrates the difference between the voltage input to the − terminal and the voltage input to the + terminal according to a time constant determined by the resistance value R of the resistor 12b and the capacitance C of the capacitor 12c, and according to the integration result. Output voltage. The comparator 13 outputs a signal when the output voltage of the integrator 12 is input to the − terminal, the + terminal is grounded, and the output voltage of the integrator 12 is equal to the ground potential. The LOGIC block 14 inputs the output of the comparator 13 and the clock. The LOGIC block 14 counts the input clock and controls the switch 11 based on a count value (hereinafter referred to as “integration time” as appropriate). When the LOGIC block 14 receives a signal from the comparator 13, the LOGIC block 14 outputs the count value (integration time) at that time as a digital value.

  The integration operation by the double integration AD converter 10 will be described with reference to FIG. FIG. 4 is a diagram showing the time change of the output of the integrator 12 of the double integration type AD converter 10. In the double integration type AD converter 10, when the AD conversion operation is started, first, the LOGIC block 14 switches the switch 11 so that the first integrated voltage Vin is input, and simultaneously starts counting the integration time. To do. When the switch 11 is switched to the first integrated voltage Vin side, the integrator 12 has a period until the count value (integration time) becomes the first count value T0 (hereinafter referred to as “first integration time T0” as appropriate). First integration (hereinafter referred to as “first integration”) is performed. During the first integration, the output of the integrator 12 decreases with a constant slope -Vin / RC as shown in FIG. When the count value (integration time) reaches the first count value T0 (first integration time T0), the LOGIC block 14 switches the switch 11 so that the second integrated voltage −Vref is input. Start counting integration time. Simultaneously with this switching, the second integration by the integrator 12 (hereinafter referred to as “second integration”) starts. The second integrated voltage −Vref is opposite in polarity to the first integrated voltage Vin. Therefore, during the second integration, the output of the integrator 12 rises with a constant slope Vref / RC. When the output of the integrator 12 returns to 0, the comparator 13 outputs a signal indicating that the output of the integrator 12 has returned to 0 to the LOGIC block 14. When receiving this signal, the LOGIC block 14 outputs a count value T (hereinafter referred to as “second integration time T” as appropriate) at that time as a digital value as an output of the AD converter 10. Since the second integrated voltage -Vref is constant, the second integration time T is a value proportional to the first integrated voltage Vin.

  The above-described double integration operation can be expressed by the following mathematical formula 1. When Formula 1 is solved and the second integration time T is arranged, Formula 2 is obtained. Since the second integrated voltage −Vref and the count value T0 are constant values, the second integration time T is a value proportional to the first integrated voltage Vin. Also, it can be seen from Equation 2 that the second integration time T does not depend on the resistance R and the capacitance C.

  In general, since the double integration type AD converter performs two integration operations of a first integration for integrating the first integrated voltage Vin and a second integration for integrating the second integrated voltage -Vref, the conversion speed is high. Although it is slower than other types of AD converters, it has a feature that it can be converted with high accuracy, and is used in applications such as digital multimeters and digital temperature sensors.

  Patent Document 1 discloses that a second integrated voltage is divided and input as a reference voltage for an integrator and a comparator of a double integration AD converter.

  In a dial-type tuning radio or the like, the reception frequency is switched by operating the dial. The dial is composed of a potentiometer, for example. The potentiometer is composed of a variable resistor whose resistance value changes with the rotation angle, for example. In order to convert the rotation amount of the potentiometer dial into a digital output using a double integral AD converter, the resistance value after the variable resistance of the potentiometer is converted into a voltage and input to the double integral AD converter. There is a need.

  As shown in FIG. 5, a method for obtaining the first integrated voltage Vin by simply passing a current from the current source 22 to the variable resistor 23 of the potentiometer 21 was studied. However, in this method, if the resistance value Rv of the variable resistor 23 or the current value I of the current flowing through the variable resistor 23 changes depending on the use environment such as manufacturing variations of the potentiometer 21 and the current source 22 and temperature, the first integrated voltage Vin. Will change. Therefore, as indicated by a broken line in FIG. 4, the slope of the first integration −Vin / RC changes, and the output of the integrator 12 of the first integration when the first integration time T0 has elapsed changes. On the other hand, since the second integrated voltage −Vref is substantially constant and the value of the gradient Vref / RC in the second integration does not change, the time until the output of the integrator 12 in the second integration becomes 0, that is, the second The integration time changes from T to T 'as shown in FIG. 4, for example. That is, even when the dial of the potentiometer 21 is rotated by the same amount, there is a problem that the second integration time varies depending on manufacturing variations and usage environments.

  This can be expressed as Equation 3 below. That is, assuming that the resistance value of the variable resistor 23 of the potentiometer 21 is Rv, the rotation amount (rotation ratio) of the potentiometer 21 is x, and the current from the current source 22 is I, the first integrated voltage Vin is Become. Substituting Equation 3 into Equation 1 yields Equation 4. That is, as can be seen from Equation 3, even if the value of x is constant, if the resistance value Rv of the variable resistor 23 of the potentiometer 21 or the current I by the current source 22 changes, the second integration time T (digital Output) value changes.

  In view of the above problems, the present invention provides a digital output that is not affected by manufacturing variations or usage environments, even when the resistance value of the potentiometer's variable resistance or the current from the current source changes due to manufacturing variations or usage environments. It is an object of the present invention to provide an AD converter, a dial-type input device, and a resistance-voltage conversion circuit that can obtain the above.

  As a first aspect of the present invention, an AD converter is provided. The AD converter includes a double integration AD converter, a variable resistor, and a resistance-voltage conversion circuit. The double integration type AD converter performs a first integration that integrates a difference voltage between the first integrated voltage and the reference voltage when the first integrated voltage is input, and after executing the first integration, An integrator for performing a second integration for integrating a difference voltage between the second integrated voltage and the reference voltage when the second integration voltage is input, and outputting an integration voltage corresponding to at least the second integration; An output unit that inputs an integration voltage and a reference voltage output from the measuring device, measures a time from when the second integration is started until the integration voltage becomes equal to the reference voltage, and outputs a digital value. . The resistance-voltage conversion circuit changes the first integrated voltage in proportion to the product of the variable resistance value of the variable resistance and the value of the current flowing through the variable resistance, and flows through the total resistance value of the variable resistance and the variable resistance. The second integrated voltage and the reference voltage are changed in proportion to the product of the current.

  As a second aspect of the present invention, a dial input device using the AD converter of the first aspect is provided.

  As a third aspect of the present invention, a resistance-voltage conversion circuit is provided. The resistance-voltage conversion circuit performs a first integration that integrates a difference voltage between the first integrated voltage and the reference voltage when the first integrated voltage is input, and after the first integration, An integrator for performing a second integration for integrating a difference voltage between the second integrated voltage and the reference voltage when two integration voltages are input, and outputting an integration voltage corresponding to at least the second integration; And an output unit that inputs the integration voltage and the reference voltage output from, measures the time from the start of the second integration until the integration voltage and the reference voltage become equal, and outputs a digital value. The double integration AD converter generates and outputs the first integrated voltage based on the resistance value of the variable resistor, and generates and outputs the second integrated voltage and the reference voltage. The resistance-voltage conversion circuit changes the first integrated voltage in proportion to the product of the variable resistance value of the variable resistance and the value of the current flowing through the variable resistance, and flows through the total resistance value of the variable resistance and the variable resistance. The second integrated voltage and the reference voltage are changed in proportion to the product of the current.

  According to the present invention, since the resistance value of the variable resistor and the value of the current flowing through the variable resistor have changed due to the influence of manufacturing variation, the use environment, etc., the resistance value after the variable resistor is varied and the value of the current flowing through the variable resistor When the first integrated voltage that is the product of the first and second integrated voltages changes, the total resistance value of the variable resistor and the variable resistance are also obtained for the second integrated voltage and the reference voltage that are input to the double integration AD converter together with the first integrated voltage. Changes in proportion to the product of the current flowing through As a result, even when the resistance value of the variable resistor and the value of the current flowing through the variable resistor change due to manufacturing variation, usage environment, etc., the time from the start of the second integration until the integration voltage becomes equal to the reference voltage The influence on the output of the digital value (hereinafter referred to as “digital output” where appropriate) is cancelled. Therefore, it is possible to obtain a digital output that is not affected by manufacturing variations and usage environments.

Configuration of dial type input device according to embodiment It is a figure which shows the time change of the integrator output of the double integral type AD converter concerning embodiment. It is a block diagram of a general double integral type AD converter. It is a figure which shows the time change of the integrator output of the conventional double integration type AD converter. It is a figure which shows the structure in the case of obtaining the 1st to-be-integrated voltage which is the input voltage of the integrator of a general double integral type AD converter by flowing an electric current through a variable resistance.

  An embodiment of the present invention will be described.

1. Configuration FIG. 1 is a configuration diagram of a dial type input device according to an embodiment. The dial type input device includes a potentiometer 41, a double integration AD converter 10, and an AD converter having a resistance-voltage conversion circuit 30. The configuration of the double integration AD converter 10 is the same as that described with reference to FIG. The integrator 12 of the double integration AD converter 10 and the + terminal of the comparator 13 are not grounded, but a reference voltage Vcom described later is input.

  The potentiometer 41 is configured using a three-terminal type variable resistor 42. The variable resistor 42 includes fixed terminals at both ends and an intermediate adjustment terminal. As the potentiometer 41, a rotary type that detects the amount of rotation is used. An operation dial is attached to the rotary shaft of the potentiometer 41. By rotating this dial, the position of the adjustment terminal of the variable resistor 42 is changed, and the resistance value between the adjustment terminal and the fixed terminals at both ends is changed. Can be made.

  The resistance-voltage conversion circuit 30 is a circuit that converts the variable resistance value of the variable resistor 42 of the potentiometer 41 into a voltage, and includes two current sources 31 and 32, an operational amplifier 33, a P-type transistor 34, and resistors 35 and 36. , 37, 38, 39. The resistance values of the resistors 35, 36, 37, 38, and 39 are set to Rc, Rc, Rs, Rr, and Rr, respectively. In this embodiment, Rs = 2Rr. The AD converter 10 and the resistance-voltage conversion circuit 30 are integrated in one integrated circuit, but may not be integrated.

  The output of the current source 31 is connected to one fixed terminal of the variable resistor 42, and the output of the current source 33 is connected to the other fixed terminal of the variable resistor 42. The two current sources 31 and 32 are constituted by a current mirror circuit and generate the same current I.

  The resistors 35 and 36 are connected in series between both fixed terminals of the variable resistor 42 of the potentiometer 41.

  The source of the P-type transistor 34 is connected to the power supply, and the output of the operational amplifier 33 is input to the gate.

  Resistors 37, 38, and 39 are connected in series from the P-type transistor 34 side between the drain of the P-type transistor 34 and the ground.

  The operational amplifier 33 has a negative terminal connected to a connection part between the two resistors 35 and 36, and a positive terminal connected to a connection part between the resistor 37 and the resistor 38.

2. Operation The operation of the dial type input device of this embodiment will be described below.
The resistance-voltage conversion circuit 30 outputs the voltage at the connection between one terminal of the variable resistor 42 and the output of the current source 32 as the first integrated voltage Vin of the double integration AD converter 10. The voltage at the connection between the drain and the resistor 37 is output as the second integrated voltage Vref of the double integration AD converter 10, and the reference voltage Vcom at the connection between the resistor 37 and the resistor 38 is output as the double integration AD converter 10. Are output to the + terminal of the operational amplifier 12 a of the integrator 12 and the + terminal of the comparator 13. What kind of voltage these voltages become will be described later.

  When receiving the first integrated voltage Vin, the second integrated voltage Vref, and the reference voltage Vcom from the resistance-voltage conversion circuit 30, the double integration AD converter 10 operates as follows. That is, the integrator 12 of the double integration type AD converter 10 has a voltage difference between the first integrated voltage Vin and the reference voltage Vcom when the first integrated voltage Vin is input from the resistance-voltage conversion circuit 30. The second integration is performed to integrate the difference voltage between the second integrated voltage Vref and the reference voltage Vcom when the second integrated voltage Vref is input after the first integration is performed. To output an integrated voltage corresponding to the integrated value. The comparator 13 receives the integrated voltage output from the integrator 12 and the reference voltage Vcom, compares them, and outputs a signal indicating that they are equal to the LOGIC block 14 when they are equal. When the LOGIC block 14 receives a signal indicating that they are equal, the LOGIC block 14 outputs the count value T (second integration time T) at that time as a digital value as an output of the AD converter 10.

  The voltage etc. of each part in this dial type input device will be described using mathematical expressions. First, when the rotation amount of the dial of the potentiometer 41 is x, the first integrated voltage Vin is expressed by the above Equation 3. Further, the voltage V− input to the − terminal of the operational amplifier 33 is expressed by Equation 5.

  In the present embodiment, the resistance value Rc of the resistors 35 and 36 is set sufficiently larger than the resistance value Rv of the variable resistor 42 of the potentiometer 41. Therefore, the voltage at the connection portion of the resistors 35, 36, that is, the voltage V− input to the − terminal of the operational amplifier 33 can be approximated by Equation 6. Further, the resistance-voltage conversion circuit 30 of the present embodiment is configured such that the − terminal and the + terminal of the operational amplifier 33 are virtually shorted. Therefore, the voltage V + input to the + terminal of the operational amplifier 33 is equal to the voltage V− of the − terminal as shown in Equation 7.

  Further, the input impedances of the + terminal and − terminal of the operational amplifier 12 a of the integrator 12 and the + terminal of the comparator 13 are high. Therefore, the reference voltage Vcom is expressed by Equation 8 and the second integrated voltage Vref is expressed by Equation 9.

  Here, in the conventional circuits of FIGS. 3 and 5, the + terminal of the integrator 12 and the + terminal of the comparator 13 are respectively grounded. However, in the circuit of FIG. The voltage Vcom is input. Therefore, the first integrated voltage is (Vcom−Vin), and the second integrated voltage is (Vref−Vcom). By replacing Vin in Formula 2 with Vcom−Vin and Vref with Vref−Vcom, the second integration time T is expressed by Formula 10 in this embodiment.

  Substituting Equations 3, 8, and 9 into Equation 10 results in Equation 11. As apparent from Equation 11, the second integration time T does not depend on the resistance value Rv of the variable resistor 42 of the potentiometer 41 and the current value I of the current sources 31 and 32, but only on the rotation rate x of the potentiometer 41. Will do. That is, even if the resistance value Rv of the variable resistor 42 and the value I of the current flowing through the variable resistor 42 change due to manufacturing variations and usage environments, the influence on the second integration time T (digital output) is cancelled. Therefore, it is possible to obtain a digital output that is not affected by manufacturing variations and usage environments.

  The first integrated voltage Vin changes in proportion to the product of the variable resistance value of the variable resistor 42 and the current value I flowing through the variable resistor 42. Therefore, Vin = α · x · Rv · I is expressed. be able to. α is a constant. On the other hand, the second integrated voltage Vref and the reference voltage Vcom change in proportion to the product of the total resistance value (resistance value between both ends) of the variable resistor 42 and the value I of the current flowing through the variable resistor 42. Therefore, Vref = β Rv · I and Vcom = γ · Rv · I can be expressed. β and γ are constants. By substituting these formulas into the formula 10, the formula 12 is obtained.

  As can be seen from this equation, the second integration time T does not depend on the resistance value Rv of the variable resistor 42 or the value I of the current flowing through the variable resistor 42, and constants α, β, γ, the rotation amount x of the variable resistor 42 , And only depends on the first integration time T0. Here, since the constants α, β, γ, and the first integration time T0 are constant, the second integration time T changes based only on the rotation amount x. That is, even if the resistance value Rv of the variable resistor 42 and the value I of the current flowing through the variable resistor 42 change due to manufacturing variations and usage environments, the influence on the digital output related to the second integration time T is cancelled. Therefore, it is possible to obtain a digital output that is not affected by manufacturing variations and usage environments.

  Note that this embodiment corresponds to the case where α = 1, β = 2, and γ = 1 in Equation 12, and when these values are substituted into Equation 12, Equation 11 can be obtained.

  FIG. 2 is a diagram illustrating a change in the output of the integrator 12. The output of the integrator 12 rises at a constant slope (Vcom−Vin) / RC during the first integration (until the first integration time time T0 elapses), and the second integration time T0 elapses. When the integration is started, it decreases at a constant slope − (Vref−Vcom) / RC. Here, even if the slope of the first integral changes from a solid line to a broken line due to manufacturing variations of the variable resistor 42 and the current sources 31 and 32 and the usage environment, the slope of the second integral also changes from the solid line to a broken line. Thus, the same second integration time T is obtained. Therefore, a constant digital output can be obtained. That is, when the dial of the potentiometer 41 is rotated by the same angle, a constant second integration time T (digital output) based only on the rotation amount x can be obtained regardless of manufacturing variations and usage environments.

3. Summary As described above, in the dial type input device (AD converter) of this embodiment, the first integrated voltage Vin is set to the product of the resistance value after the variable resistor 42 is variable and the value of the current I flowing through the variable resistor 42. The second integrated voltage Vref and the reference voltage Vcom are changed in proportion to the product of the total resistance value Rv (resistance value between both ends) of the variable resistor 42 and the current I flowing through the variable resistor 42. Thereby, the second integration time T changes based only on the rotation amount x. That is, even if the resistance value Rv of the variable resistor 42 and the value I of the current flowing through the variable resistor 42 change due to manufacturing variations and usage environments, the influence on the digital output related to the second integration time T is cancelled. Therefore, it is possible to obtain a digital output that is not affected by manufacturing variations and usage environments.

  Further, since the resistance-voltage conversion circuit 30 and the double integration AD converter 10 are integrated in one integrated circuit, the external component may be only a variable resistor. Therefore, cost can be reduced.

  In addition, since the two current sources 31 and 32 are configured by current mirror circuits, two current sources that allow the same current to flow can be configured with a simple circuit.

  Moreover, since the dial type input device of the present embodiment includes the resistance-voltage conversion circuit 30 as described above, it is possible to obtain a high-precision digital output corresponding to the dial scale.

  In the present embodiment, the case where a rotary type potentiometer that detects the amount of rotation is used as the potentiometer has been described. However, the present invention can also be applied to the case where a linear type potentiometer that detects a linear movement amount is used.

  In the present embodiment, the case where α = 1, β = 2, and γ = 1 in Formula 12 is described, but this is an example, and α, β, and γ may be other values.

  According to the AD converter, the dial input device, and the resistance-voltage conversion circuit according to the present invention, it is possible to obtain a digital output that is not affected by manufacturing variations and usage environments. The AD converter according to the present invention can be widely used in an AD converter using a double integral AD converter.

DESCRIPTION OF SYMBOLS 10 Double integral type AD converter 11 Switch 12 Integrator 13 Comparator 14 LOGIC block 30 Resistance-voltage conversion circuit 31 Current source 32 Current source 33 Operational amplifier 34 P-type transistor 35 Resistance 36 Resistance 37 Resistance 38 Resistance 39 Resistance 41 Potentiometer 42 Variable resistance

JP 05-083135 A

Claims (7)

When a first integrated voltage is input, a first integration is performed to integrate a difference voltage between the first integrated voltage and a reference voltage. After the first integration is performed, a second integrated voltage is input. An integrator that performs a second integration that integrates a difference voltage between the second integrated voltage and a reference voltage and outputs an integration voltage corresponding to at least the second integration, and an output from the integrator. An integration voltage and the reference voltage to be input, an output unit that measures the time from the start of the second integration until the integration voltage and the reference voltage become equal and outputs a digital value; A double integral AD converter with
Variable resistance,
The first integrated voltage is changed in proportion to the product of the variable resistance value of the variable resistor and the value of the current flowing through the variable resistor, and the total resistance value of the variable resistor and the current flowing through the variable resistor are A resistance-voltage conversion circuit that changes the second integrated voltage and the reference voltage in proportion to a product;
Equipped with a,
The variable resistor is
It has a fixed terminal at both ends and a grounded adjustment terminal,
The resistance-voltage conversion circuit is:
Two current sources for flowing current to the fixed terminals at both ends of the variable resistor;
Two resistors connected in series between fixed terminals at both ends of the variable resistor;
A voltage generation unit that generates a first voltage and a second voltage proportional to a voltage generated at a connection portion between the two resistors;
A voltage at one fixed terminal of the variable resistor is output as the first integrated voltage;
Outputting the first voltage as the second integrated voltage;
Outputting the second voltage as the reference voltage;
An AD converter characterized by that. The resistance - voltage converter circuit AD converter of claim 1 Symbol mounting, characterized in that it is integrated into one integrated circuit. It said two current source AD converter according to claim 1 or 2, wherein it is configured by a current mirror circuit. The dial type input device using the AD converter of any one of Claim 1 to 3 . When a first integrated voltage is input, a first integration is performed to integrate a difference voltage between the first integrated voltage and a reference voltage. After the first integration is performed, a second integrated voltage is input. An integrator that performs a second integration that integrates a difference voltage between the second integrated voltage and a reference voltage and outputs an integration voltage corresponding to at least the second integration, and an output from the integrator. An integration voltage and the reference voltage to be input, an output unit that measures the time from the start of the second integration until the integration voltage and the reference voltage become equal and outputs a digital value; Resistor that generates and outputs the first integrated voltage based on the resistance value of the variable resistor and generates and outputs the second integrated voltage and the reference voltage to the double integral AD converter provided A voltage conversion circuit comprising:
The first integrated voltage is changed in proportion to the product of the variable resistance value of the variable resistor and the value of the current flowing through the variable resistor, and the total resistance value of the variable resistor and the current flowing through the variable resistor are Changing the second integrated voltage and the reference voltage in proportion to a product ;
The variable resistor is
It has a fixed terminal at both ends and a grounded adjustment terminal,
The resistance-voltage conversion circuit is:
Two current sources for flowing current to the fixed terminals at both ends of the variable resistor;
Two resistors connected in series between fixed terminals at both ends of the variable resistor;
A voltage generation unit that generates a first voltage and a second voltage proportional to a voltage generated at a connection portion between the two resistors;
A voltage at one fixed terminal of the variable resistor is output as the first integrated voltage;
Outputting the first voltage as the second integrated voltage;
Outputting the second voltage as the reference voltage;
Resistance wherein a call - voltage converter circuit. The resistance - voltage converter circuit that claim 5 Symbol mounting of the resistor, characterized in that is integrated into a single integrated circuit - voltage converter circuit. It said two current source resistor of claim 5 or 6, wherein it is configured by a current mirror circuit - voltage converter circuit.

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